Ten veterans who did not develop posttraumatic stress after intense
combat in Vietnam were studied to explain what had protected them. The
authors found a highly consistent adaptation to combat: During combat each
of these veterans had exhibited calmness under pressure, intellectual
control, acceptance of fear, and a lack of excessively violent or
guilt-arousing behavior. The authors believe that these traits may be part
of an adaptation uniquely suitable for preserving emotional stability in an
unstructured, unstable context.